This proposal seeks to elucidate the structure and function of iron-containing enzymes involved in oxygen activation. Moreover, it is proposed to study a variety of Fe(IV) containing synthetic compounds that mimic structural and electronic features of the active sites of the enzymes under study. Further, it is proposed to study the Mossbauer spectra of proteins in overexpressing E. coli cells. The experimental techniques employed are Mossbauer spectroscopy, Electron paramagnetic resonance (EPR) and SQUID magnetometry. It is also proposed to study high-valent Fe(IV) sites of proteins and model complexes with density functional theory. [unreadable] [unreadable] (1) Studies of the diiron proteins methane monooxygenase, ribonucleotide reductase, delta9 desaturase and phenolhydroxylase will be continued. [unreadable] (2) This research will be complemented by studies of model complexes to gain insight into the electronic structure of the active sites of the enzymes. [unreadable] (3) Whole-cell studies of iron containing proteins overexpressed in E. coli will be continued. [unreadable] (4) The Mossbauer and EPR spectra of compound I of cytochrome P450 isolated from a thermophilic bacterium will be studied. [unreadable] (5) Mossbauer and EPR studies of four non-heme iron proteins suspected to pass in their catalytic cycles through an Fe(IV)=O intermediate will be performed. [unreadable] (6) Iron(IV) sites occurring in enzymes and model complexes will be investigated with density functional theory. [unreadable] [unreadable]